Oakland Athletics pitcher Daniel Mengden (67) throws against the San Francisco Giants during the fifth inning of a baseball game, Monday, June 27, 2016 in San Francisco. Mengden earned his first major-league win. He pitched 7 2/3 innings. He allowed four hits, two runs and struck out five. Jeff ChiuThe Associated Press

Oakland Athletics pitcher Daniel Mengden (67) throws against the San Francisco Giants during the fifth inning of a baseball game, Monday, June 27, 2016 in San Francisco. Mengden earned his first major-league win. He pitched 7 2/3 innings. He allowed four hits, two runs and struck out five. Jeff ChiuThe Associated Press

Mengden earns first big-league win, A’s beat Giants 8-3

A few minutes after the A’s 8-3 win over the Giants on Monday night, catcher Stephen Vogt emerged from the A’s clubhouse and jogged back down a flight of stairs leading to the visiting dugout.

“Mengden, let’s go!” Vogt yelled.

Starting pitcher Daniel Mengden, who had just recorded his first major-league win, was still on the field being interviewed. After a moment, he appeared at the top of the stairs and moved quickly through the clubhouse door followed closely by Vogt, already shaking a canin his right hand.

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So the A’s had to wait a little to deliver the traditional first-win beer shower. Mengden had already waited – through three starts where he pitched well enough to earn the win but fell victim to a lack of support. Monday night, the A’s spotted him five runs in the second inning, Mengden held a streaking Giants team scoreless until the eighth, and the result was, finally, a milestone moment for the 23-year-old.

“The usual just first-win, dump stuff all over me and celebrate,” Mengden said of the shower. “It felt good. It was really cold.”

Mengden froze the Giants’ bats for the better part of Monday’s opener of this four-game Bay Bridge Series. He did not allow a baserunner until Angel Pagan hit a one-out single in the fifth inning. He sailed through the first three innings on 36 pitches, striking out four and snaring Gregor Blanco’s liner up the middle to end the second inning with a reflexive jolt of his glove hand.

“That caught me, I didn’t catch that,” Mengden said. “I was trying to duck out of the way.”

Mengden became just the third A’s starter this season to pitch into the eighth inning and had allowed just two singles to that point. He lost his shutout in the eighth as the Giants loaded the bases with no outs and reliever Chris Stratton grounded into a double play, driving in a run. Mengden then walked Joe Panik, his second walk of the inning on his 104th pitch, which ended his night.

As he walked to the dugout, Mengden received a standing ovation from some of the A’s fans at AT&T Park – who made up the majority of the crowd left at that point, given the A’s held an 8-1 lead.

“He pitched really like he has his three previous outings,” A’s manager Bob Melvin said. “Got a little bit tired at the end there, but we’ve basically seen the same guy that’s efficient, throws strikes with all four pitches, keeps you off-balance, confident in what he’s doing. It’s been really fun to watch.”

In his first three starts, Mengden had allowed six runs in 18 innings but taken three losses while receiving just two runs of support. This time, he was pitching with a cushion by the third inning as the A’s tagged right-hander Jeff Samardzija for five runs in the second, three coming on Marcus Semien’s 15th home run of the season.

The A’s acquired Semien before the 2015 season by trading Samardzija to the White Sox, something of which Semien said he was well aware.

“Oh yeah, every time I face him I know that’s a guy I got traded for,” Semien said. “We’ve had some good games against him. Anytime we face him, we want to try to do that every time, that’s our goal no matter who it is. But (Chris) Bassitt, (Josh) Phegley and I wouldn’t be here if we didn’t get traded for him, and I’ll always know that.”

Mengden was acquired by the A’s in last summer’s trade deadline deal of Scott Kazmir to the Astros. Going into this season, he was expected to spend 2016 in the minors, but was fast-tracked to Oakland by a rash of injuries in the starting rotation. “From the day he got here, he looked like he belonged and he looked like he had presence out on the mound and was in charge,” Melvin said. “It’s basically been the same game each time, maybe a little bit better today. But boy, it’s been really impressive.”

Still, even as Mengden was shutting down the Giants on Monday night, starter Rich Hill was making a rehab start for Single-A Stockton, on the path to returning from a strained groin. Sean Manaea, currently on the disabled list with a strained pronator muscle in his forearm, is expected to start against the Giants on Wednesday.

When those pitchers return to the A’s rotation, where will that leave Mengden?

“You keep performing, you’ll find a place for yourself,” Melvin said. “We’ll see how it all shakes out, but he continues to perform.”